It is now known that small changes in bone adaption to mechanical load can lead to large changes in[unreadable] skeletal resistance to fracture. Osteocytes are believed to be the mechanosensory cells of bone receiving[unreadable] these physiological signals and responding in a manner to regulate their local microenvironment and to[unreadable] globally control bone formation and bone resorption in selective regions of bone. Dentin Matrix Protein 1,[unreadable] DMP1, and Matrix Extracellular Phosphoglycoprotein, MEPE, are highly expressed in osteocytes and[unreadable] respond to mechanical load. Both proteins are highly localized in the canaliculi and lacunae of osteocytes,[unreadable] with DMP1 found predominately on the canalicular walls. Our goal is to use these two genes as[unreadable] representative of osteocyte selective genes responsive to mechanical strain to identify molecular signalling[unreadable] mechanisms responsible for changes in bone properties. Our hypothesis is that specific osteocyte selective[unreadable] and mechanically responsive enhancer regions exist in the promoters of DMP1 and MEPE that are[unreadable] controlled by specific transcription family pathways in response to strain. To test this hypothesis three[unreadable] specific aims are proposed: Specific Aim 1. Determine the relationship between DMP1 and MEPE gene[unreadable] expression patterns with strain field analysis upon mechanical loading in vivo. Specific Aim 2. Determine[unreadable] the relationship of osteocyte deformation in the mouse ulna and femur to different levels of strain and gene[unreadable] activation of the DMP1 and MEPE cis-regulatory regions. Specific Aim 3. Determine the cis-regulatory[unreadable] regions of the DMP1 and MEPE genes that control the response to loading selectively in osteocytes. This[unreadable] project is unique in that DMP1 and MEPE gene expression will be correlated with macroscopic strain in vivo[unreadable] and with local cell deformation ex vivo. These genes and their appropriate cis-regulatory regions linked to[unreadable] reporters will serve as sensitive read-outs of osteocyte responsiveness in different loading conditions in[unreadable] different genetic backgrounds. This project will be devoted to understanding the cis-regulatory systems of[unreadable] both the DMP1 and MEPE genes in terms of their osteocyte selectivity and to identifying transcription factors[unreadable] responsible for this selectivity and responsiveness to mechanical loading. The goals of this project will be[unreadable] accomplished using cell models to identify molecular mechanisms, animal models for in vivo validation,[unreadable] together with engineering principles, combined with a molecular and a systems biology approach.[unreadable] Increased fatigue resistance is a major means to prevent fracture. Mapping osteocyte genes and[unreadable] pathways that are selectively responsive to load will provide information important to prevention or treatment[unreadable] of bone disease such as disuse osteoporosis, post menopausal osteoporosis and other pathological[unreadable] conditions of bone loss.